1. Field of the Invention
The present invention relates to an optical communication system, and more particularly, to a recovery system performing a 3R (re-timing, re-shaping, re-amplifying) function on an optical signal.
2. Description of the Related Art
During the transmission of an optical signal via an optical cable in an optical communication system, the size of the signal is reduced and the signal is transformed due to the occurrence of diffusion, and thus, the distortion of the signal is unavoidable in optical communication. In order to recover the transformed optical signal into its original state, a 3R (re-timing, re-shaping, re-amplifying) function should be performed, and a 3R recovery system for performing a 3R function is an essential element for establishing a network.
Re-timing, that is, clock recovery, of a 3R function is the extracting of a clock signal from a transformed optical signal and recovering of a signal from the clock signal and the transformed optical signal using a decision circuit. A clock signal can be extracted by using an electrical phase locked loop (PLL) circuit or full light recovery. The electrical PLL circuit has limited speed.
Conventionally, in full 3R recovery, a clock recovery device and a decision device, respectively, for 2R (re-shaping and re-amplifying) are manufactured so that the full 3R function is completed using optical coupling. Due to the optical coupling of the clock recovery device and the decision device, a coupling loss is inevitably generated. Functions of controlling polarization and delay are additionally required such that the structure of a 3R recovery system is complicated.